Engineering curves

ENGINEERING CURVES
Part- I {Conic Sections}
ELLIPSE
1.Concentric Circle Method
2.Rectangle Method
3.Oblong Method
4.Arcs of Circle Method
5.Rhombus Metho
6.Basic Locus Method
(Directrix – focus)
HYPERBOLA
1.Rectangular Hyperbola
(coordinates given)
2 Rectangular Hyperbola
(P-V diagram - Equation given)
PARABOLA
1.Rectangle Method
2 Method of Tangents
( Triangle Method)
Methods of Drawing
Tangents & Normals
To These Curves.

CONIC SECTIONS
ELLIPSE, PARABOLA AND HYPERBOLA ARE CALLED CONIC SECTIONS
BECAUSE
THESE CURVES APPEAR ON THE SURFACE OF A CONE
WHEN IT IS CUT BY SOME TYPICAL CUTTING PLANES.
Section PlaneSection Plane
Through GeneratorsThrough Generators
EllipseEllipse
Section Plane ParallelSection Plane Parallel
to end generator.to end generator.
Parabola
Parabola
Section PlaneSection Plane
Parallel to Axis.Parallel to Axis.
HyperbolaHyperbola
OBSERVE
ILLUSTRATIONS
GIVEN BELOW..

These are the loci of points moving in a plane such that the ratio of it’s distances
from a fixed point And a fixed line always remains constant.
The Ratio is called ECCENTRICITY. (E)
A) For Ellipse E<1
B) For Parabola E=1
C) For Hyperbola E>1
SECOND DEFINATION OF AN ELLIPSE:-
It is a locus of a point moving in a plane
such that the SUM of it’s distances from TWO fixed points
always remains constant.
{And this sum equals to the length of major axis.}
These TWO fixed points are FOCUS 1 & FOCUS 2
Refer Problem nos. 6. 9 & 12
Refer Problem no.4
Ellipse by Arcs of Circles Method.
COMMON DEFINITION OF ELLIPSE, PARABOLA & HYPERBOLA:

1
2
3
4
5
6
7
8
9
10
BA
D
C
1
2
3
4
5
6
7
8
9
10
Steps:
1. Draw both axes as perpendicular bisectors
of each other & name their ends as shown.
2. Taking their intersecting point as a center,
draw two concentric circles considering both
as respective diameters.
3. Divide both circles in 12 equal parts &
name as shown.
4. From all points of outer circle draw vertical
lines downwards and upwards respectively.
5.From all points of inner circle draw
horizontal lines to intersect those vertical
lines.
6. Mark all intersecting points properly as
those are the points on ellipse.
7. Join all these points along with the ends of
both axes in smooth possible curve. It is
required ellipse.
Problem 1 :-
Draw ellipse by concentric circle method.
Take major axis 100 mm and minor axis 70 mm long.
ELLIPSE
BY CONCENTRIC CIRCLE METHOD

1
2
3
4
1 2 3 4
1
2
3
4
3 2 1A B
C
D
Problem 2
Draw ellipse by Rectangle method.
Take major axis 100 mm and minor axis 70 mm long.
Steps:
1 Draw a rectangle taking major
and minor axes as sides.
2. In this rectangle draw both
axes as perpendicular bisectors
of each other..
3. For construction, select upper
left part of rectangle. Divide
vertical small side and horizontal
long side into same number of
equal parts.( here divided in four
parts)
4. Name those as shown..
5. Now join all vertical points
1,2,3,4, to the upper end of minor
axis. And all horizontal points
i.e.1,2,3,4 to the lower end of
minor axis.
6. Then extend C-1 line upto D-1
and mark that point. Similarly
extend C-2, C-3, C-4 lines up to
D-2, D-3, & D-4 lines.
7. Mark all these points properly
and join all along with ends A
and D in smooth possible curve.
Do similar construction in right
side part.along with lower half of
the rectangle.Join all points in
smooth curve.
It is required ellipse.
ELLIPSE
BY RECTANGLE METHOD

C
D
1
2
3
4
1 2 3 4 3 2 1A B
1
2
3
4
Problem 3:- Draw ellipse by Oblong method.
Draw a parallelogram of 100 mm and 70 mm long
sides with included angle of 750.
Inscribe Ellipse in it.
STEPS ARE SIMILAR TO
THE PREVIOUS CASE
(RECTANGLE METHOD)
ONLY IN PLACE OF RECTANGLE,
HERE IS A PARALLELOGRAM.
ELLIPSE
BY OBLONG METHOD

F1 F2
1 2 3 4
A B
C
D
p1
p2
p3
p4
ELLIPSE
BY ARCS OF CIRCLE METHOD
O
PROBLEM 4.
MAJOR AXIS AB & MINOR AXIS CD ARE
100 AMD 70MM LONG RESPECTIVELY
.DRAW ELLIPSE BY ARCS OF CIRLES
METHOD.
STEPS:
1.Draw both axes as usual.Name the
ends & intersecting point
2.Taking AO distance I.e.half major
axis, from C, mark F1 & F2 On AB .
( focus 1 and 2.)
3.On line F1- O taking any distance,
mark points 1,2,3, & 4
4.Taking F1 center, with distance A-1
draw an arc above AB and taking F2
center, with B-1 distance cut this arc.
Name the point p1
5.Repeat this step with same centers but
taking now A-2 & B-2 distances for
drawing arcs. Name the point p2
6.Similarly get all other P points.
With same steps positions of P can be
located below AB.
7.Join all points by smooth curve to get
an ellipse/
As per the definition Ellipse is locus of point P moving in
a plane such that the SUM of it’s distances from two fixed
points (F1 & F2) remains constant and equals to the length
of major axis AB.(Note A .1+ B .1=A . 2 + B. 2 = AB)

1
4
2
3
A B
D C
ELLIPSE
BY RHOMBUS METHOD
PROBLEM 5.
DRAW RHOMBUS OF 100 MM & 70 MM LONG
DIAGONALS AND INSCRIBE AN ELLIPSE IN IT.
STEPS:
1. Draw rhombus of given
dimensions.
2. Mark mid points of all sides &
name Those A,B,C,& D
3. Join these points to the ends of
smaller diagonals.
4. Mark points 1,2,3,4 as four
centers.
5. Taking 1 as center and 1-A
radius draw an arc AB.
6. Take 2 as center draw an arc CD.
7. Similarly taking 3 & 4 as centers
and 3-D radius draw arcs DA & BC.

ELLIPSE
DIRECTRIX-FOCUS METHOD
PROBLEM 6:- POINT F IS 50 MM FROM A LINE AB.A POINT P IS MOVING IN A PLANE
SUCH THAT THE RATIO OF IT’S DISTANCES FROM F AND LINE AB REMAINS CONSTANT
AND EQUALS TO 2/3 DRAW LOCUS OF POINT P. { ECCENTRICITY = 2/3 }
F ( focus)
DIRECTRIX
V
ELLIPSE
(vertex)
A
B
STEPS:
1 .Draw a vertical line AB and point F
50 mm from it.
2 .Divide 50 mm distance in 5 parts.
3 .Name 2nd
part from F as V. It is 20mm
and 30mm from F and AB line resp.
It is first point giving ratio of it’s
distances from F and AB 2/3 i.e 20/30
4 Form more points giving same ratio such
as 30/45, 40/60, 50/75 etc.
5.Taking 45,60 and 75mm distances from
line AB, draw three vertical lines to the
right side of it.
6. Now with 30, 40 and 50mm distances in
compass cut these lines above and below,
with F as center.
7. Join these points through V in smooth
curve.
This is required locus of P.It is an ELLIPSE.
30mm
45mm

1
2
3
4
5
6
1 2 3 4 5 6
1
2
3
4
5
6
5 4 3 2 1
PARABOLA
RECTANGLE METHOD
PROBLEM 7: A BALL THROWN IN AIR ATTAINS 100 M HIEGHT
AND COVERS HORIZONTAL DISTANCE 150 M ON GROUND.
Draw the path of the ball (projectile)-
STEPS:
1.Draw rectangle of above size and
divide it in two equal vertical parts
2.Consider left part for construction.
Divide height and length in equal
number of parts and name those
1,2,3,4,5& 6
3.Join vertical 1,2,3,4,5 & 6 to the
top center of rectangle
4.Similarly draw upward vertical
lines from horizontal1,2,3,4,5
And wherever these lines intersect
previously drawn inclined lines in
sequence Mark those points and
further join in smooth possible curve.
5.Repeat the construction on right side
rectangle also.Join all in sequence.
This locus is Parabola.
.

1
2
3
4
5
6
7
8
9
10
11
12
13
14 1
2
3
4
5
6
7
8
9
10
11
12
13
14
C
A B
PARABOLA
METHOD OF TANGENTS
Problem no.8: Draw an isosceles triangle of 100 mm long base and
110 mm long altitude.Inscribe a parabola in it by method of tangents.
Solution Steps:
1. Construct triangle as per the given
dimensions.
2. Divide it’s both sides in to same no.of
equal parts.
3. Name the parts in ascending and
descending manner, as shown.
4. Join 1-1, 2-2,3-3 and so on.
5. Draw the curve as shown i.e.tangent to
all these lines. The above all lines being
tangents to the curve, it is called method
of tangents.

A
B
V
PARABOLA
(VERTEX)
F
( focus)
4 3 2 1 1 2 3 4
PARABOLA
DIRECTRIX-FOCUS METHOD
SOLUTION STEPS:
1.Locate center of line, perpendicular to
AB from point F. This will be initial
point P.
2.Mark 5 mm distance to its right side,
name those points 1,2,3,4 and from those
draw lines parallel to AB.
3.Mark 5 mm distance to its left of P and
name it 1.
4.Take F-1 distance as radius and F as
center draw an arc
cutting first parallel line to AB. Name
upper point P1
and lower point P2
.
5.Similarly repeat this process by taking
again 5mm to right and left and locate
P3
P4
.
6.Join all these points in smooth curve.
It will be the locus of P equidistance
from line AB and fixed point F.
PROBLEM 9: Point F is 50 mm from a vertical straight line AB.
Draw locus of point P, moving in a plane such that
it always remains equidistant from point F and line AB.

P
O
40 mm
30 mm
1
2
3
12 1 2 3
1
2
HYPERBOLA
THROUGH A POINT
OF KNOWN CO-ORDINATES
SSolution Steps:
Extend horizontal line from P to
right side.
2Extend vertical line from P upward.
3On horizontal line from P, mark
some points taking any distance and
name them after P-1, 2,3,4 etc.
4Join 1-2-3-4 points to pole O. Let
them cut part [P-B] also at 1,2,3,4
points.
5From horizontal 1,2,3,4 draw
vertical lines downwards and
6From vertical 1,2,3,4 points [from
P-B] draw horizontal lines.
7Line from 1 horizontal and line from
1 vertical will meet at P1
.Similarly
mark P2
, P3
, P4
points.
8Repeat the procedure by marking
four points on upward vertical line
from P and joining all those to pole
O. Name this points P6
, P7
, P8
etc. and
join them by smooth curve.
Problem No.10: Point P is 40 mm and 30 mm from horizontal
and vertical axes respectively.Draw Hyperbola through it.

VOLUME:( M3
)
PRESSURE
(Kg/cm2
)
0 1 2 3 4 5 6 7 8 9 10
1
2
3
4
5
6
7
8
9
10 HYPERBOLA
P-V DIAGRAM
Problem no.11: A sample of gas is expanded in a cylinder
from 10 unit pressure to 1 unit pressure.Expansion follows
law PV=Constant.If initial volume being 1 unit, draw the
curve of expansion. Also Name the curve.
Form a table giving few more values of P & V
P V = C
+
10
5
4
2.5
2
1
1
2
2.5
4
5
10
10
10
10
10
10
10
++++++
=
=
=
=
=
=
Now draw a Graph of
Pressure against Volume.
It is a PV Diagram and it is Hyperbola.
Take pressure on vertical axis and
Volume on horizontal axis.

F ( focus)V
(vertex)
A
B
30mm
45mm
HYPERBOLA
DIRECTRIX
FOCUS METHOD
PROBLEM 12:- POINT F IS 50 MM FROM A LINE AB.
A POINT P IS MOVING IN A PLANE SUCH THAT THE RATIO
OF IT’S DISTANCES FROM F AND LINE AB REMAINS
CONSTANT AND EQUALS TO 2/3
DRAW LOCUS OF POINT P. { ECCENTRICITY = 2/3 }
STEPS:
1 .Draw a vertical line AB and point F
50 mm from it.
2 .Divide 50 mm distance in 5 parts.
3 .Name 3rd part from F as V. It is 30 mm
and 20 mm from F and AB line resp.
It is first point giving ratio of it’s
distances from F and AB = 3/2 i.e 30/20
4 Form more points giving same ratio such
as 45/30, 60/40, 75/50 etc.
5.Taking 30. 40 and 50 mm distances from
line AB, draw three vertical lines to the
right side of it.
6. Now with 45, 60 and 75 mm distances in
compass cut these lines above and
below, with F as center.
7. Join these points through V in smooth
curve.
This is required locus of P. It is Hyperbola.

D
F1 F2
1 2 3 4
A B
C
p1
p2
p3
p4
O
Q TANGENT
NORMAL
TO DRAW TANGENT & NORMAL
TO THE CURVE FROM A GIVEN POINT ( Q )
1. JOIN POINT Q TO F1 & F2
2. BISECT ANGLE F1Q F2 THE ANGLE BISECTOR IS NORMAL
3. A PERPENDICULAR LINE DRAWN TO IT IS TANGENT TO THE CURVE.
ELLIPSE
TANGENT & NORMAL
Problem 13:

ELLIPSE
TANGENT & NORMAL
F ( focus)
DIRECTRIX
V
ELLIPSE
(vertex)
A
B
T
T
N
N
Q
900
TO THE CURVE
FROM A GIVEN POINT ( Q )
1.JOIN POINT Q TO F.
2.CONSTRUCT 900 ANGLE WITH
THIS LINE AT POINT F
3.EXTEND THE LINE TO MEET DIRECTRIX
AT T
4. JOIN THIS POINT TO Q AND EXTEND. THIS IS
TANGENT TO ELLIPSE FROM Q
5.TO THIS TANGENT DRAW PERPENDICULAR
LINE FROM Q. IT IS NORMAL TO CURVE.
Problem 14:

A
B
PARABOLA
VERTEX F
( focus)
V
Q
T
N
N
T
900
TO THE CURVE
2.CONSTRUCT 900
ANGLE WITH
THIS LINE AT POINT F
3.EXTEND THE LINE TO MEET DIRECTRIX
AT T
TANGENT TO THE CURVE FROM Q
PARABOLA
TANGENT & NORMAL
Problem 15:

F ( focus)V
(vertex)
A
B
HYPERBOLA
TANGENT & NORMAL
QN
N
T
T
900
TO THE CURVE
2.CONSTRUCT 900
ANGLE WITH THIS LINE AT
POINT F
3.EXTEND THE LINE TO MEET DIRECTRIX AT T
TANGENT TO CURVE FROM Q
Problem 16

INVOLUTE CYCLOID SPIRAL HELIX
ENGINEERING CURVES
Part-II
(Point undergoing two types of displacements)
1. Involute of a circle
a)String Length = πD
b)String Length > πD
c)String Length < πD
2. Pole having Composite
shape.
3. Rod Rolling over
a Semicircular Pole.
1. General Cycloid
2. Trochoid
( superior)
3. Trochoid
( Inferior)
4. Epi-Cycloid
5. Hypo-Cycloid
1. Spiral of
One Convolution.
2. Spiral of
Two Convolutions.
1. On Cylinder
2. On a Cone
Methods of Drawing
Tangents & Normals
To These Curves.
AND

CYCLOID:
IS A LOCUS OF A POINT ON THE
ERIPHERY OF A CIRCLE WHICH
OLLS ON A STRAIGHT LINE PATH.
NVOLUTE:
IS A LOCUS OF A FREE END OF A STRING
HEN IT IS WOUND ROUND A CIRCULAR POLE
SPIRAL:
IS A CURVE GENERATED BY A POINT
HICH REVOLVES AROUND A FIXED POINT
ND AT THE SAME MOVES TOWARDS IT.
HELIX:
IS A CURVE GENERATED BY A POINT WHICH
OVES AROUND THE SURFACE OF A RIGHT CIRCULAR
YLINDER / CONE AND AT THE SAME TIME ADVANCES IN AXIAL DIRECTION
T A SPEED BEARING A CONSTANT RATIO TO THE SPPED OF ROTATION.
or more problems on helix refer topic Development of surfaces)
DEFINITIONS
SUPERIORTROCHOID:
IF THE POINT IN THE DEFINATION
OF CYCLOID IS OUTSIDE THE
CIRCLE
INFERIOR TROCHOID.:
IF IT IS INSIDE THE CIRCLE
EPI-CYCLOID
IF THE CIRCLE IS ROLLING ON
ANOTHER CIRCLE FROM OUTSIDE
HYPO-CYCLOID.
IF THE CIRCLE IS ROLLING FROM
INSIDE THE OTHER CIRCLE,

INVOLUTE OF A CIRCLE
Problem no 17: Draw Involute of a circle.
String length is equal to the circumference of circle.
1 2 3 4 5 6 7 8
P
P8
1
2
3
4
5
6
7
8
P3
3
to
p
P4
4 to p
P5
5to
p
P7
7
to
p
P6
6top
P2
2top
P1
1to
p
π
D
A
Solution Steps:
1) Point or end P of string AP is
exactly πD distance away from A.
Means if this string is wound round
the circle, it will completely cover
given circle. B will meet A after
winding.
2) Divide πD (AP) distance into 8
number of equal parts.
3)  Divide circle also into 8 number
of equal parts.
4)  Name after A, 1, 2, 3, 4, etc. up
to 8 on πD line AP as well as on
circle (in anticlockwise direction).
5)  To radius C-1, C-2, C-3 up to C-8
draw tangents (from 1,2,3,4,etc to
circle).
6)  Take distance 1 to P in compass
and mark it on tangent from point 1
on circle (means one division less
than distance AP).
7)  Name this point P1
8)  Take 2-B distance in compass
and mark it on the tangent from
point 2. Name it point P2.
9)  Similarly take 3 to P, 4 to P, 5 to
P up to 7 to P distance in compass
and mark on respective tangents
and locate P3, P4, P5 up to P8 (i.e.
A) points and join them in smooth
curve it is an INVOLUTE of a given
circle.

String length MORE than πD
1 2 3 4 5 6 7 8
P
1
2
3
4
5
6
7
8
P3
3
to
p
P4
4 to p
P5
5to
p
P7
7
to
p
P6
6top
P2
2top
P1
1to
p
165 mm
(more than πD)
πD
p8
Solution Steps:
In this case string length is more
than Π D.
But remember!
Whatever may be the length of
string, mark Π D distance
horizontal i.e.along the string
and divide it in 8 number of
equal parts, and not any other
distance. Rest all steps are same
as previous INVOLUTE. Draw
the curve completely.
Problem 18: Draw Involute of a circle.
String length is MORE than the circumference of circle.

1 2 3 4 5 6 7 8
P
1
2
3
4
5
6
7
8
P3
3
to
p
P4
4 to p
P5
5to
p
P7
7
to
p
P6
6top
P2
2top
P1
1top
150 mm
(Less than πD)
πD
String length LESS than πD
Problem 19: Draw Involute of a circle.
String length is LESS than the circumference of circle.
Solution Steps:
In this case string length is Less
than Π D.
But remember!
Whatever may be the length of
string, mark Π D distance
horizontal i.e.along the string
and divide it in 8 number of
equal parts, and not any other
distance. Rest all steps are same
as previous INVOLUTE. Draw
the curve completely.

1
2
34
5
6
1 2 3 4 5 6
A
P
πD/2
P1
1toP
P2
2
to
P
P3
3 to P
P4
4toP
P
AtoPP5
5toP
P6
6toP
INVOLUTE
OF
COMPOSIT SHAPED POLE
PROBLEM 20 : A POLE IS OF A SHAPE OF HALF HEXABON AND SEMICIRCLE.
ASTRING IS TO BE WOUND HAVING LENGTH EQUAL TO THE POLE PERIMETER
DRAW PATH OF FREE END P OF STRING WHEN WOUND COMPLETELY.
(Take hex 30 mm sides and semicircle of 60 mm diameter.)
SOLUTION STEPS:
Draw pole shape as per
dimensions.
Divide semicircle in 4
parts and name those
along with corners of
hexagon.
Calculate perimeter
length.
Show it as string AP.
On this line mark 30mm
from A
Mark and name it 1
Mark πD/2 distance on it
from 1
And dividing it in 4 parts
name 2,3,4,5.
Mark point 6 on line 30
mm from 5
Now draw tangents from
all points of pole
and proper lengths as
done in all previous
involute’s problems and
complete the curve.

1
2
3
4
πD
1
2
3
4
A
B
A1
B1
A2
B2
A3
B3
A4
B4
PROBLEM 21 : Rod AB 85 mm long rolls
over a semicircular pole without slipping
from it’s initially vertical position till it
becomes up-side-down vertical.
Draw locus of both ends A & B.
Solution Steps?
If you have studied previous problems
properly, you can surely solve this also.
Simply remember that this being a rod,
it will roll over the surface of pole.
Means when one end is approaching,
other end will move away from poll.
OBSERVE ILLUSTRATION CAREFULLY!

P
C1 C2 C3 C4 C5 C6 C7 C8
p1
p2
p3
p4
p5
p6
p7
p8
1
2
3
4
5
6
7
C
πD
CYCLOID
PROBLEM 22: DRAW LOCUS OF A POINT ON THE PERIPHERY OF A CIRCLE
WHICH ROLLS ON STRAIGHT LINE PATH. Take Circle diameter as 50 mm
Solution Steps:
1)      From center C draw a horizontal line equal to πD distance.
2)      Divide πD distance into 8 number of equal parts and name them C1, C2, C3__ etc.
3)      Divide the circle also into 8 number of equal parts and in clock wise direction, after P name 1, 2, 3 up to 8.
4)      From all these points on circle draw horizontal lines. (parallel to locus of C)
5)      With a fixed distance C-P in compass, C1 as center, mark a point on horizontal line from 1. Name it P.
6)      Repeat this procedure from C2, C3, C4 upto C8 as centers. Mark points P2, P3, P4, P5 up to P8 on the
horizontal lines drawn from 2, 3, 4, 5, 6, 7 respectively.
7)      Join all these points by curve. It is Cycloid.

C1 C2 C3 C4 C5 C6 C7 C8
p1
p2
p3
p4
p5
p6
p7
p8
1
2
3
4
5
6
7
C
πD
SUPERIOR TROCHOID
P
PROBLEM 23: DRAW LOCUS OF A POINT , 5 MM AWAY FROM THE PERIPHERY OF A
CIRCLE WHICH ROLLS ON STRAIGHT LINE PATH. Take Circle diameter as 50 mm
Solution Steps:
1)      Draw circle of given diameter and draw a horizontal line from it’s center C of length Π D and divide it
in 8 number of equal parts and name them C1, C2, C3, up to C8.
2)      Draw circle by CP radius, as in this case CP is larger than radius of circle.
3)      Now repeat steps as per the previous problem of cycloid, by dividing this new circle into 8 number of
equal parts and drawing lines from all these points parallel to locus of C and taking CP radius wit
different positions of C as centers, cut these lines and get different positions of P and join
4)      This curve is called Superior Trochoid.

P
C1 C2 C3 C4 C5 C6 C7 C8
p1
p2
p3
p4
p5
p6
p7
p8
1
2
3
4
5
6
7
C
πD
INFERIOR TROCHOID
PROBLEM 24: DRAW LOCUS OF A POINT , 5 MM INSIDE THE PERIPHERY OF A
CIRCLE WHICH ROLLS ON STRAIGHT LINE PATH. Take Circle diameter as 50 mm
Solution Steps:
1)      Draw circle of given diameter and draw a horizontal line from it’s center C of length Π D and divide it
in 8 number of equal parts and name them C1, C2, C3, up to C8.
2)      Draw circle by CP radius, as in this case CP is SHORTER than radius of circle.
3)      Now repeat steps as per the previous problem of cycloid, by dividing this new circle into 8 number
of equal parts and drawing lines from all these points parallel to locus of C and taking CP radius
with different positions of C as centers, cut these lines and get different positions of P and join
those in curvature.
4)      This curve is called Inferior Trochoid.

C
C1
C2
C3 C4
C
5
C
8
C6
C7
EPI CYCLOID :
P
O
R
r = CP
+
r
R
3600
=
1
2
3
4 5
6
7
Generating/
Rolling Circle
Directing Circle
Solution Steps:
1)  When smaller circle will roll on
larger circle for one revolution it will
cover Π D distance on arc and it will be
decided by included arc angle θ.
2)  Calculate θ by formula θ = (r/R) x
3600.
3)  Construct angle θ with radius OC
and draw an arc by taking O as center
OC as radius and form sector of angle
θ.
4)  Divide this sector into 8 number of
equal angular parts. And from C
onward name them C1, C2, C3 up to
C8.
5)  Divide smaller circle (Generating
circle) also in 8 number of equal parts.
And next to P in clockwise direction
name those 1, 2, 3, up to 8.
6)  With O as center, O-1 as radius
draw an arc in the sector. Take O-2, O-
3, O-4, O-5 up to O-8 distances with
center O, draw all concentric arcs in
sector. Take fixed distance C-P in
compass, C1 center, cut arc of 1 at P1.
Repeat procedure and locate P2, P3,
P4, P5 unto P8 (as in cycloid) and join
them by smooth curve. This is EPI –
CYCLOID.
WHICH ROLLS ON A CURVED PATH. Take diameter of rolling Circle 50 mm
And radius of directing circle i.e. curved path, 75 mm.

HYPO CYCLOID
C
P1
P2
P3
P4
P5
P6 P7
P8
P
1
2
3
6
5
7
4
C1
C2 C3
C4
C
5
C
6
C
7
C8
O
OC = R ( Radius of Directing Circle)
CP = r (Radius of Generating Circle)
+
r
R
3600
=
WHICH ROLLS FROM THE INSIDE OF A CURVED PATH. Take diameter of
rolling circle 50 mm and radius of directing circle (curved path) 75 mm.
Solution Steps:
1)  Smaller circle is rolling
here, inside the larger
circle. It has to rotate
anticlockwise to move
ahead.
2)  Same steps should be
taken as in case of EPI –
CYCLOID. Only change is
in numbering direction of 8
number of equal parts on
the smaller circle.
3)  From next to P in
anticlockwise direction,
name 1,2,3,4,5,6,7,8.
4)  Further all steps are
that of epi – cycloid. This
is called
HYPO – CYCLOID.

7 6 5 4 3 2 1
P
1
2
3
4
5
6
7
P2
P6
P1
P3
P5
P7
P4 O
SPIRAL
Problem 27: Draw a spiral of one convolution. Take distance PO 40 mm.
Solution Steps
1. With PO radius draw a circle
and divide it in EIGHT parts.
Name those 1,2,3,4, etc. up to 8
2 .Similarly divided line PO also in
EIGHT parts and name those
1,2,3,-- as shown.
3. Take o-1 distance from op line
and draw an arc up to O1 radius
vector. Name the point P1
4. Similarly mark points P2, P3, P4
up to P8
And join those in a smooth curve.
It is a SPIRAL of one convolution.
IMPORTANT APPROACH FOR CONSTRUCTION!
FIND TOTAL ANGULAR AND TOTAL LINEAR DISPLACEMENT
AND DIVIDE BOTH IN TO SAME NUMBER OF EQUAL PARTS.

16 13 10 8 7 6 5 4 3 2 1 P
1,9
2,10
3,11
4,12
5,13
6,14
7,15
8,16
P1
P2
P3
P4
P5
P6
P7
P8
P9
P10
P11
P12
P13 P14
P15
SPIRAL
of
two convolutions
Problem 28
Point P is 80 mm from point O. It starts moving towards O and reaches it in two
revolutions around.it Draw locus of point P (To draw a Spiral of TWO convolutions).
IMPORTANT APPROACH FOR CONSTRUCTION!
FIND TOTAL ANGULAR AND TOTAL LINEAR DISPLACEMENT
AND DIVIDE BOTH IN TO SAME NUMBER OF EQUAL PARTS.
SOLUTION STEPS:
Total angular displacement here
is two revolutions And
Total Linear displacement here
is distance PO.
Just divide both in same parts i.e.
Circle in EIGHT parts.
( means total angular displacement
in SIXTEEN parts)
Divide PO also in SIXTEEN parts.
Rest steps are similar to the previous
problem.

Tangent
Normal
Q
Involute
Method of Drawing
Tangent & Normal
STEPS:
DRAW INVOLUTE AS USUAL.
MARK POINT Q ON IT AS DIRECTED.
JOIN Q TO THE CENTER OF CIRCLE C.
CONSIDERING CQ DIAMETER, DRAW
A SEMICIRCLE AS SHOWN.
MARK POINT OF INTERSECTION OF
THIS SEMICIRCLE AND POLE CIRCLE
AND JOIN IT TO Q.
THIS WILL BE NORMAL TO INVOLUTE.
DRAW A LINE AT RIGHT ANGLE TO
THIS LINE FROM Q.
IT WILL BE TANGENT TO INVOLUTE.
1 2 3 4 5 6 7 8
P
P8
1
2
3
4
5
6
7
8
π
D
C

Q
N Normal
Tangent
CYCLOID
Method of Drawing
Tangent & Normal
STEPS:
DRAW CYCLOID AS USUAL.
MARK POINT Q ON IT AS DIRECTED.
WITH CP DISTANCE, FROM Q. CUT THE
POINT ON LOCUS OF C AND JOIN IT TO Q.
FROM THIS POINT DROP A PERPENDICULAR
ON GROUND LINE AND NAME IT N
JOIN N WITH Q.THIS WILL BE NORMAL TO
CYCLOID.
DRAW A LINE AT RIGHT ANGLE TO
THIS LINE FROM Q.
IT WILL BE TANGENT TO CYCLOID.
P
C1 C2 C3 C4 C5 C6 C7 C8
πD
CYCLOID
C
CP

7 6 5 4 3 2 1
P
1
2
3
4
5
6
7
P2
P6
P1
P3
P5
P7
P4 O
SPIRAL (ONE CONVOLUSION.)
Normal
Tangent
Q
Spiral.
Method of Drawing
Tangent & Normal
Constant of the Curve =
Difference in length of any radius vectors
Angle between the corresponding
radius vector in radian.
OP – OP2
π/2
OP – OP2
1.57
= 3.185 m.m.
==
STEPS:
*DRAW SPIRAL AS USUAL.
DRAW A SMALL CIRCLE OF RADIUS EQUAL TO THE
CONSTANT OF CURVE CALCULATED ABOVE.
* LOCATE POINT Q AS DISCRIBED IN PROBLEM AND
THROUGH IT DRAW A TANGENTTO THIS SMALLER
CIRCLE.THIS IS A NORMAL TO THE SPIRAL.
*DRAW A LINE AT RIGHT ANGLE
*TO THIS LINE FROM Q.
IT WILL BE TANGENT TO CYCLOID.

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